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Background While many studies have found an association between irritable bowel syndrome (IBS) and obesity, many others did not. Hence, this systematic review with meta-analysis aims to evaluate the relationship between obesity and IBS, and determine whether obesity correlates differently with the various IBS endotypes. Methods A systematic review of published literature was conducted in concordance with the PRISMA guidelines and followed by a meta-analysis of relevant studies using the random-effects model. The 34 included studies assessed obesity among non-IBS controls and IBS subjects, either as continuous or dichotomous outcomes, using body mass index (BMI) and waist circumference (WC). The standardized mean difference (SMD) and 95% confidence interval (CI); and the odds ratio (OR) and 95% CI were obtained for continuous and dichotomous outcomes respectively. Meta-regression was performed to identify sources of heterogeneity. Results We found a weak association between IBS and obesity, but this was not statistically significant. For BMI, the overall SMD was +0.227 (95% CI: –0.093 to 0.547, p = 0.164) and OR was 1.312 (95% CI: 0.974 to 1.767, p = 0.074). For WC, the overall SMD was +1.020 cm (95% CI: –1.768 to 3.807, p = 0.473). However, subgroup analysis revealed significantly higher BMI among IBS-diarrhoea (IBS-D) subjects compared to controls (SMD = +1.940; 95% CI: 0.679 to 3.200, p = 0.003) and significantly lower BMI among IBS-constipation (IBS-C) subjects compared to IBS-D subjects (SMD = –1.720; 95% CI: –2.489 to –0.950, p Conclusions In conclusion, our systematic review with meta-analysis showed that obesity is positively associated with diarrhoea-predominant IBS, but not IBS in general. Our findings support the exploration of shared pathophysiology between IBS-D and obesity.